1. Field of the Invention
The present invention relates to a method and a circuit for controlling rotation speed of a computer fan.
2. Description of Related Art
Generally, a computer system includes a motherboard with various chips such as a central processing unit (CPU) mounted thereon, a storage device such as a hard disc, and input/output devices, each of which is known to generate heat when operated in a computer system, especially the CPU. If the heat generated from the CPU is not dissipated in a timely fashion, it may damage the CPU or even the computer system.
Typically, a sensor is programmed to be used as a temperature detector for detecting temperature of the CPU. A computer fan is used to facilitate removal of heat to keep the temperature of the CPU within a safe temperature range. A fan controller is provided to adjust fan speed to be more energy efficient while still providing enough heat dissipation. The computer fan includes 3-pin fans, which can be adjusted by a voltage signal and 4-pin fans, which can be adjusted by a pulse-width modulation (PWM) signal controlled by a basic input/output system (BIOS) of the motherboard.
In a 3-pin fan motherboard, a 3-pin fan is connected to the motherboard by a 3-pin header mounted on the motherboard, and a 3-pin fan controller is provided to supply the voltage signal to the 3-pin fan for adjusting the rotation speed of the 3-pin fan. In a 4-pin fan motherboard, a 4-pin fan is connected to the motherboard by a 4-pin fan header mounted on the motherboard in which the fourth pin is used to transmit the PWM signal, and a 4-pin fan controller is provided to supply the PWM signal to the 4-pin fan for adjusting the rotation speed of the 4-pin fan. However, though the 3-pin fan can be connected to the 4-pin fan motherboard by the 4-pin header, it cannot be controlled by the 4-pin fan controller because the 3-pin fan does not have the fourth pin and cannot receive the PWM signal. Therefore, the CPU may be damaged because the heat may not be dissipated properly.
What is needed, therefore, is to provide a method and a circuit which can adjust the rotation speed of a computer fan whether the computer fan is a 3-pin fan or a 4-pin fan.